The present invention relates to a digital-to-analog converter and to a method for facilitating outputting of an analog output of predetermined value from the digital-to-analog converter in response to a digital input code.
Digital-to-analog converters (DACs) which are formed as integrated circuits typically are formed by mass-production processes. In such mass-production processes, while it is possible to maintain the parameters of the internal circuits within such DACs substantially constant, nonetheless, drift from DAC to DAC in a mass production process does take place. Thus, a predetermined analog output value will not always result from a corresponding predetermined digital input code from one DAC to the next For example, the analog resistance output value of a resistive DAC for a given digital input code may vary from resistive DAC to resistive DAC due to drift in the production process. To put the problem another way, a known digital input code will not always produce the same analog resistance output value from one resistive DAC to the next. While in many applications for resistive DACs, this variation from DAC to DAC may be acceptable. However, in certain applications this variation is unacceptable. This is particularly so in cases where a resistive DAC is required to produce an analog resistance output of specific predetermined value for a predetermined digital input code, and in particular, where a resistive DAC is required to produce a range of analog resistance outputs of respective specific predetermined values for a corresponding range of predetermined digital input codes. Similar problems arise in respect of other DACs, for example, voltage DACs and current DACs.
There is therefore a need for a DAC which facilitates outputting of an analog output of predetermined value from a predetermined digital input code, and there is also a need for a method for facilitating the outputting of such an analog output of predetermined value from a DAC in response to a predetermined digital input code.
The present invention is directed towards providing such a DAC and a method.
According to the invention there is provided A DAC comprising:
an input port for receiving a digital input code,
an output port for outputting an analog output corresponding to a digital input code on the input port,
a digit-to-analog converting means for converting digital input codes received from the input port to corresponding analog outputs for outputting on the output port,
a storing means for storing a transfer coefficient of the DAC, the transfer coefficient being a function by which the digital input codes should be altered to produce respective corresponding analog outputs of respective predetermined values, and
a communicating means for facilitating reading of the transfer coefficient from the storing means.
In one embodiment of the invention the transfer coefficient is a constant over a range of digital input codes. Preferably, the transfer coefficient is a constant for all digital input codes for which the DAC is adapted to receive.
In one embodiment of the invention the transfer coefficient is the function by which the respective digital input codes should be multiplied to produce the respective corresponding analog outputs of predetermined values.
Preferably, the transfer coefficient is stored as a digital code.
In one embodiment of the invention the communicating means communicates the storing means with the input port for facilitating reading of the transfer coefficient from the storing means by an external reading means through the input port. Ideally, the communicating means facilitates writing of the transfer coefficient to the storing means through the input port.
In one embodiment of the invention the DAC is a resistive DAC for providing analog resistance outputs in response to corresponding digital input codes.
In another embodiment of the invention the DAC is formed as an integrated circuit, and the storing means is formed in the integrated circuit.
In a further embodiment of the invention a plurality of transfer coefficients are stored the storing means, the transfer coefficients corresponding to respective segments of the range of digital input codes for which the DAC is adapted to receive, and the transfer coefficients being stored with their respective corresponding segments.
Additionally, the invention provides a method for facilitating outputting of an analog output of predetermined value from a DAC corresponding to a digital input code, the method comprising storing a transfer coefficient in the DAC, the transfer coefficient being a function by which digital input codes to the DAC should be altered to produce respective corresponding analog outputs of respective predetermined values, the transfer coefficient being stored so that it can be read and digital input codes to the DAC can be appropriately altered by the transfer coefficient to produce corresponding analog outputs of desired respective predetermined values.
In one embodiment of the invention the transfer coefficient is a constant over a range of digital input codes. Preferably, the transfer coefficient is a constant for all digital Input codes for which the DAC is adapted to receive.
In one embodiment of the invention the transfer coefficient is the function by which the respective digital input codes should be multiplied to produce the respective corresponding analog outputs of predetermined values.
Preferably, the transfer coefficient is stored as a digital code.
In another embodiment of the invention the method further comprises the step of writing the transfer coefficient to a storing means in the DAC.
Preferably, the method further comprises the step of determining the transfer coefficient by applying at least one digital input code of known value to the DAC which should produce an analog output of known predetermined value if the DAC were an ideal DAC, recording the actual value of the analog output produced by the known digital input code, and dividing the known predetermined value of the analog output which should have been produced by the known digital input code by the actual value of the analog output produced by the known digital input code, and the resulting value being thee transfer coefficient.
In one embodiment of the invention the transfer coefficient is determined by applying a plurality of digital codes of known values to the DAC, and recording the corresponding actual value of the analog outputs produced by the respective known digital input codes, and determining a plurality of transfer coefficients from the respective actual values of the analog outputs produced and their corresponding predetermined analog values, and determining the average transfer coefficient from the respective transfer coefficients, and storing the average transfer coefficient.
Alternatively, a plurality of transfer coefficients are determined for respective segments of the range of digital input codes which the DAC is adapted to receive, and the respective coefficients are stored together with the respective segments to which they correspond.
In another embodiment of the invention the DAC is formed as an integrated circuit, and a storing means for storing the transfer coefficient is formed in the integrated circuit.
The advantages of the invention are many. In particular, the DAC according to the invention permits analog outputs of predetermined values to be outputted in response to corresponding predetermined digital input codes. This is achieved by virtue of the fact that a transfer coefficient is determined for the DAC, and the transfer coefficient is stored in a storing means in the DAC, so that it can be read and the value of the predetermined digital input code which should produce the analog output of predetermined value can be altered by the transfer coefficient so that the analog output of the desired predetermined value is outputted from the DAC.
The invention will be more clearly understood from the following description of some preferred embodiments thereof which are given by way of example only with reference to the accompanying drawings.